Add documentation about how to run terraform-plugin-docs in debug mode

### Terraform CLI and terraform-plugin-docs Versions

github.com/hashicorp/terraform-plugin-docs v0.24.0 // indirect

### Use Cases or Problem Statement

It would be helpful to be able to have a debug mode while running tfplugindocs. Not only using it as a binary but having the ability to call it as a library to enable easier debugging setup in an IDE.
In particular that would be helpful to contribute more to the code.

### Proposal

Exporting the internal/cmd package outside of the internal folder

### How much impact is this issue causing?

High

### Additional Information

_No response_

### Code of Conduct

- [x] I agree to follow this project's Code of Conduct